Three-dimensional vortex formation on a heaving low-aspect-ratio wing: Computations and experiments

This paper addresses by means of high-resolution numerical simulations and experimental quantitative imaging the three-dimensional unsteady separation process induced by large-amplitude heaving oscillations of a low-aspect-ratio wing under low-Reynolds-number conditions. Computed results are found to be in good agreement with experimental flow visualizations and PIV measurements on selected cross-flow planes. The complex unsteady three-dimensional flow structure generated during dynamic stall of the low-aspect-ratio wing is elucidated. The process is characterized by the generation of a leading-edge vortex system which is pinned at the front corners of the plate and which exhibits intense transverse flow toward the wing centerline during its initial stages of development. This vortex detaches from the corners and evolves into an newly found arch-type structure. The legs of the arch vortex move along the surface toward the wing centerline and reconnect forming a ring-like structure which is shed as the next plunging cycle begins. Vortex breakdown, total collapse and reformation of the wing tip vortices are also observed at various stages of the heaving motion. At the relatively high value of reduced frequency considered, these basic flow elements of the complex three-dimensional dynamic stall process are found to persist over a range of Reynolds numbers.